Question

Which sugar is present in DNA? (a) purine only (b) deoxyribose (c) ribose (d) pyrimidine only

Short answer

The sugar present in DNA is deoxyribose, option (b).

Step-by-step solution

Understand DNA Structure

DNA, or deoxyribonucleic acid, is a molecule that carries genetic information in living organisms. Understanding the components of DNA is essential for identifying the sugar present in its structure.

Identify the Components of DNA

DNA is composed of a phosphate backbone, sugar, and four nitrogenous bases (adenine, thymine, cytosine, and guanine). The sugar present in DNA is a key structural component.

Distinguish Between DNA and RNA Sugars

The sugar in DNA is deoxyribose, while the sugar in RNA, or ribonucleic acid, is ribose. The presence of deoxyribose differentiates DNA from RNA, which contains ribose sugar.

Eliminate Incorrect Options

Purines and pyrimidines are not sugars; they are nitrogenous bases. Therefore, the options (a) purine only and (d) pyrimidine only can be eliminated. Option (c) ribose is the sugar found in RNA, not DNA.

Select the Correct Option

The sugar present in DNA is deoxyribose. Thus, the correct answer is (b) deoxyribose.

Key concepts

DNA structure

Deoxyribonucleic acid, commonly known as DNA, is the hereditary material that contains the instructions necessary for the growth, development, and reproduction of all living organisms. The structure of DNA is often compared to a twisted ladder or double helix. At its core, the DNA molecule is composed of three main components: a sugar called deoxyribose, a phosphate group, and four nitrogenous bases.
The sugar and phosphate molecules form the sides of the ladder, creating the DNA backbone. This backbone supports the sequence of nitrogenous bases that form the rungs of the ladder. The nitrogenous bases are paired specifically: adenine pairs with thymine, and cytosine pairs with guanine. Together, these components help encode the information DNA carries. Understanding the structure of DNA is crucial, as it reveals how genetic information is replicated and transmitted across generations.

DNA vs RNA

DNA and RNA are both essential nucleic acids in biology, yet they serve different roles and have distinct structures. Both are polymers made up of nucleotides, but each has unique features that set them apart.
- **Sugar Component:** DNA contains a sugar called deoxyribose, whereas RNA has ribose sugar. The absence of one oxygen atom in deoxyribose makes DNA more stable compared to RNA. - **Structure:** DNA generally exists as a double-stranded helix, while RNA is usually single-stranded. - **Bases:** DNA uses thymine as one of its nitrogenous bases, while RNA uses uracil instead. - **Function:** DNA is primarily responsible for storing and transferring genetic information, whereas RNA plays various roles like acting as a messenger between DNA and protein synthesis machinery or as a catalyst in some reactions. These differences reflect the varied tasks the two molecules undertake in the cell, with DNA serving as a long-term storage of genetic information and RNA working actively in the synthesis and regulation of proteins.

Nitrogenous bases in DNA

Nitrogenous bases are critical to the structure and function of DNA, as they form the code that carries genetic information. In DNA, there are four different nitrogenous bases, which are divided into two categories: purines and pyrimidines.
- **Purines:** Adenine (A) and Guanine (G) are the two purine bases in DNA. They are characterized by a two-ring structure. - **Pyrimidines:** Thymine (T) and Cytosine (C) are pyrimidine bases, recognized by their single-ring structure. - **Base Pairing:** The bases adhere to specific pairing rules, where adenine pairs with thymine using two hydrogen bonds, and guanine pairs with cytosine using three hydrogen bonds. This pairing is essential because it allows DNA strands to be complementary, facilitating accurate replication and transcription of genetic material. The precise arrangement of these bases forms the genetic code, which is read in three-nucleotide sequences known as codons. Each codon specifies an amino acid, the building blocks of proteins, thus playing a central role in translating the genetic script into physical traits and functions.